44 



CLIMATIC CYCLES AND TREE GROWTH 



with vertical axis. The lens focuses the cylindrical pattern on an analyzing 

 plate illustrated at 22b (and Plate 15A) whose transparent lines are inclined 

 about 17° to the vertical. The geometrical relation of the parallel lines 

 on the analyzing plate and the cylindrical pattern falling upon them are 

 shown in figure 24, page 45. As the mirror moves, the size of the cylindrical 

 pattern changes and rows of maxima coming through the analyzing plate 

 look as if they were rotating about an axis. This is merely the change (al- 



Scale 



\ ft 



U Cycleplot 



Analyzing _ 

 plate ^j 



^"Cylindrical lens 



Movable 

 mirrors 



CL 



Fig. 22 — Important parts of the cyclograph. 



a. Schematic elevation. 



b. Analyzing plate. 



most instantaneous) from one "basic" cycle length to another (see Plate 15B; 

 see also Appendix. 



Cycleplots — Many improvements have taken place in the plots prepared 

 for analysis. The original multiple plot was cut out of white paper and 

 mounted on a black background. The first cyclograms in 1914 were made 

 from a plot cut through black paper; tissue paper was placed over the open- 

 ings and lights mounted at the back. A small photographic negative or 

 positive of this was tried and found unworkable. The plot was then cut 



